the document is too big in size, that GIMP could not blur it, how should I do ?

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At a size of 2592 x 4768 you should be able to use small amounts of gaussian blur on a relatively modern computer without problems. I can on my old computer. Perhaps you are trying to blur it too much at once? Try blurring at 5-10 pixels and see if that works: it should be quicker than blurring at 500 pixels. You can repeatedly blur it in smaller amounts rather than trying to over-blur at once. Or just use the blur tool to blur it by hand.

If your computer is too old to blur at all a simple image of 2592 x 4768 pixels, you need to work at a MUCH smaller scale, as you will have increasing problems as you create your map and it gets denser and more complex. Try working at 2592 x 2384 (you can always make two maps of this size and then stick them together in the end) and see how that goes.

At a size of 2592 x 4768 you should be able to use small amounts of gaussian blur on a relatively modern computer without problems. I can on my old computer. Perhaps you are trying to blur it too much at once? Try blurring at 5-10 pixels and see if that works: it should be quicker than blurring at 500 pixels. You can repeatedly blur it in smaller amounts rather than trying to over-blur at once. Or just use the blur tool to blur it by hand.

If your computer is too old to blur at all a simple image of 2592 x 4768 pixels, you need to work at a MUCH smaller scale, as you will have increasing problems as you create your map and it gets denser and more complex. Try working at 2592 x 2384 (you can always make two maps of this size and then stick them together in the end) and see how that goes.

the thing is I tried to blur it in 4768pixels, but it doesn't have the blur effect at all, just the coastline color became light but the effect from the tutorial

I'm not sure I understand the problem. You are trying to blur the image using Gaussian Blur and you entered in the little box a (whopping) 4,768 pixels. Then you pressed ok and your computer froze? Or actually it seems that the image became so blurred that you couldn't see anything at all?

In either case, don't blur something by 4,768 pixels at once. Instead, try blurring it 500px and see how that looks, then repeat as necessary. I had a look at RoB A's very good tutorial, and he just says (in post 6) that you need to Apply a Gaussian Blur (Filter->Blue->Gaussian Blur) large enough to eliminate the absolute black and whites of the image. So do 500px once, then again if that was not enough, and so on until you have a nice smooth image full of greys.

I'm not sure I understand the problem. You are trying to blur the image using Gaussian Blur and you entered in the little box a (whopping) 4,768 pixels. Then you pressed ok and your computer froze? Or actually it seems that the image became so blurred that you couldn't see anything at all?

In either case, don't blur something by 4,768 pixels at once. Instead, try blurring it 500px and see how that looks, then repeat as necessary. I had a look at RoB A's very good tutorial, and he just says (in post 6) that you need to Apply a Gaussian Blur (Filter->Blue->Gaussian Blur) large enough to eliminate the absolute black and whites of the image. So do 500px once, then again if that was not enough, and so on until you have a nice smooth image full of greys.

oh, actually, the blur problem was solved, but I do have another question i'll be so appreciate if you can help in this thread, it is also from the same tutorial

when I was going through "Post 4: I have an idea – part 2" , in the second last step of this section, the author said to------------ :"Now Invert the selection (Select->Invert), create a new black layer called “Land Mask” and fill the selection with white. Now save the selection to a Channel (Select->Save to Channel) and rename the channel to “Land Mask”. ----------------

I had no idea where to create a new black layer, I tried "transparency" "white" "background" "foreground" none of them give me the black ground, so led to the failure of "save to channel" part, that

Good question - I think this is due to a change in Gimp as it was upgraded. In the older version, whenever you made a new layer it gave you the options of 'white, black or transparent'. In the latest versions it is called 'foreground, background or transparent'. Assuming black is your default foreground colour and white is your default background colour, you can see that it's pretty much the same.

In your case, make sure that black is selected as either a foreground or background BEFORE you make this new layer. Then, make a new layer (it does not matter whether this is at the top or at the bottom of your layers because it is just temporary) and in the options select either foreground or background colour - whichever is currently black. The new layer will appear filled with black. And then you just fill your inverted-sea selection with white, so that all the land goes white and the sea stays black.

Good question - I think this is due to a change in Gimp as it was upgraded. In the older version, whenever you made a new layer it gave you the options of 'white, black or transparent'. In the latest versions it is called 'foreground, background or transparent'. Assuming black is your default foreground colour and white is your default background colour, you can see that it's pretty much the same.

In your case, make sure that black is selected as either a foreground or background BEFORE you make this new layer. Then, make a new layer (it does not matter whether this is at the top or at the bottom of your layers because it is just temporary) and in the options select either foreground or background colour - whichever is currently black. The new layer will appear filled with black. And then you just fill your inverted-sea selection with white, so that all the land goes white and the sea stays black.

sorry to ask you again, but I'm so bad at the computer skill, I couldn't find where is the option to select colors for the Foreground and Background layer